Telephone system



NOV. 5, 1929. WALLACE 1,734,355

TELEPHONE SYSTEM Filed Dec. 20,1926 2 Sheets-Sheet 1 B. A. WALLACE 1,734,355

TELEPHONE SYSTEM Filed Dec. 20, 1926 2 Sheets-Sheet 2 721/5177 01". .EFZHDZ/llape.

Patented Nov. 5, 1929 UNITED STATES PATENT OFFICE BERT A. WALLACE, OF CHICAGO, ILLINOIS, ASSIGNOR TO KELLOGG- SWITCHBOARD AND SUPPLY COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS TELEPHONE SYSTEM Application filed December 20, 1926. Serial No. 155,815.

My invention relates to telephone systems and ha to do more particularly with systems for interconnecting lines terminating at dif-k ferent exchanges and has for its object, a novel and improved circuit arrangement.

In systems of the above character a call originating at a common battery exchange will be answered in the usual manner and through the medium of a cord circuit, provided with the well known instantaneous disconnect and line lamp recall means, may be extended to another substation located in the same exchange or may also be used to complete connections direct to tell lines for connections between a local subscriber at one exchange and a subscriber at a distant exchange. Means are provided in the said cord circuit which function when a calling subscriber recalls on a local to tell connection to switch from instantaneous disconnect with line lamp recall to a flashing recall appearing only before the original operator so that she may properly time and supervise the eon- .nection or take care of the wants of the recalling subscriber.

Another feature of my invention is the provision of a listening key in association with the keyless listening of the cord which provides means for permitting the operator to cut in only on local to tell connections for supervision purposes and when answering a recall on a connection of this kind.

For a more complete understanding of my invention reference may be had to the accompanying drawings which comprise Figs. 1 and 2. Fig. 2 when placed to the right of Fig. 1

illustrates a complete circuit arrangement for extending a connection from a subscriber at a common battery exchange to a subscriber in a distant exchange. Referring now particularly to Fig. 1, I illustrate at the left of the drawing a calling common battery sub station A terminating at the local exchange E in a line circuit L, comprising a line relay LR, cut oil relay CO and multiple answering jacks J. associated with the multiple line lamps S. Thejacks J and lamps S appear before a plurality of operators and a call initiated at the substation A Will appear before a plurality of operators as is well understood.

The cord circuit C for interconnecting a pair of local lines at the exchange E or for extending a connection to a distant exchange comprises an answering plug AP and a calling plug OP connected by the heavily marked conductors. The answering C comprises a sleeve relay SL which is energized when the answering plug AP is inserted into the jack J of the calling line to conncct the operators set 0 to the cord conductors. An answering supervisory relay SR and an answering supervisory lamp AS are jillOVlClGil for the uuual supervisory purposes. The calling end of the cord circuit C comprises sleeve relays SL and SL the said sleeve relay SL energizing when connection is made with either a local line or with a. trunk leading to a distant exchange. The sleeve relay SL also energizes when connection is made with a local called line but does not energize when a connection is made with a trunk leading to a distant exchange for purposes as will be more fully hereinafter described. I

An auxiliary sleeve relay AU is provided which energizes upon the energization of the relay SL to disconnect the operators set 0 from the cord conductors. A ringing interrupter relay RI, a ringing control relay RC and a party line ringing key RK associated with the ringing generators G, G, G and G provide means for signalling the called for subscriber on a local connection as is well understood and also used for signalling an operator at a distant exchange as will be more fully hereinafter described. A calling supervisory relay SR and a calling supervisory lamp OS are provided for the usual supervisory purposes. A flashing supervisory signal control relay FOR is provided which controls the flashing of the supervisory signal AS to indicate recall to the operator of a calling subscriber on a local to toll connection and a listening key LK is also provided which permits the operator at. the local exchange to connect her set to the cord conductor on such a connection so she may properly time and supervise'a local to toll connection and to permit her to answer a recall in response to the flashing recall signal on such a conend of the cord should she actuate herlistening key LK. The closing of alternate contact 32 of relay AU closes a circuit for the calling supervisory lamp CS traced from battery through the lamp CS, normal contact 33 of ringing control relay RC, conductors 3st and 35, normal contact 3b of link disconnect relay LD, conductor 3T,'normal contact 38 of supervisory relay SR, conductors 39, i0 and 41 to ground at alternate contact 32 of relay AU. The lamp CS is lighted over this circuit and remains lighted until the operator depresses the ringing key to signal the called for subscriber at substation B. i

The operator now signals the subscriber at substation B by depressing one or the ringlng key plunger-s of the party line ringing key RK to connect ringing current of the proper frequency to operate the call signal at the called substation B. Assumingthat the generator G is of the selected frequency the key plunger associated with this generator is moved to its fully depressed position, in which position the end spring contacts l2 of the ringing key RK are also closed. The closure of contactelQ of the end spring contacts establishes an energizing circuit for the ringing interrupter relay R-l traced from battery through the winding 4?; cl relay RI, conductor 44, alternate contact fl-2 of the end spring contacts, conductors l5 and 35, normal contact 36 of relay LD, conductor 37, normal contact 38, conductors 39,410 and all to ground at alternate contact 32 of relay AU. The relay RI energizes and closes its alternate contact 46 thus establishing an energizing circuit for the ringing control relay RC traced from battery through the relay RC, conductor 47, alternate contact 46 of relay RI, conductor 48, alternate contact 49 of relay SL conductors and 35, normal contact 36 of relay LD, conductor 3?, normal contact 38, conductors 89, l0 and 41 to ground at alternate contact 32 of relay AU. The relay RC energizes and opens its normal contact 33 to ell'ace the signal CS and the closing of its alternate contact establishes a locking circuit for itsell traced from battery through the Winding of relay RC, its alternate contact 33,conductors 34: and 35, normal contact 86, to ground at alternate contact 32 of relay AU over the previously described path. The relay RT upon on ergization, as just described, closes its alternate contact 50 to connect ringing current from the selected generator G which may be traced from the ungrounded pole of the generator G through the closed contact 51 of the depressed key plunger, conductor 52, al ternate contact 50 of relay Bl, tip contacts of the plug GP and acl: J through the call bell and condenser at the called substation B 9 back through the ring contacts ot the ack J and plug GP to ground at alternate contact 53 of relay RT. The instantthat the ringing key plunger is depressed and the end springs 42 tacts at a position and the end spring contact is also opened but as the relay is now locked in an energized condition independent of alternate contact all or relay the closure of alternate contact of relay RC connects the constantly rotating interrupter I in circuit with the interrupts relay Ill traced from battery through the upper Winding of relay RI, conductor 56, alternate contact 54 of relay R1 to ground through the constantly rotating interrupter I. The relayRI is alternately energized and deencrgizcd over this circuit to connect ringing current to the called line to intermittently signal the called subscriber at the substation B, and the path for the ringing current from the generator G to the substation B is the same as previously described. a

The subscriber at the substation B in response to his call signal removes his receiver from the switchhook and when the relay R1 is in a deenergizcd condition which is during a silent period of a ringing cycle and energizing circuit is established for the supervisory relay SR, traced from battery througl'i the lower Winding of relay SR, conductor 5?, ring conductor of the cord C, normal contact 53 of relay RI, ring conductors or the plug P and jack tl'irough the now closed couthe substation switchhook back through the tip contacts of the jack .7 and plug GP, normal contact 50 of relay Bl, tip conductor of the cord C, conductor 58, alter nate cont-act of relay AU, conductor (30, to ground through the upper winding of relay Sll. The relay SR energizes and opens its normal contact 38 which opens the locking circuit of the relay RC and the relay RC upon deenergization opens its alternate contact 54c and the opening of the contact 5i disconnects the interru iter I from the winding 55 of the relay t1 and the relay RI new remains at normal and prevents further application of ringing current to the called line. The calling subscriber at the substation A and the called subscriber at the substation B are now in conversational circuit which may be traced over the heavily marked conductors.

Upon the termination of conversation the subscribers at the stations A and B replace their receivers upon their respective switchhoolrs. The replacing oi the receiver at the substation A opens the energizing circuit of the supervisory relay SE at the switchhook contacts and the relay SR upon deenergization closes its normal contact 61 establishing a circuit for the answering supervisory lamp AS traced from battery at normal contact of relay FOR, through the lamp AS, conductors 63, 6eland normal contact 61 of relay AS, conductor 66, normal contact 67 of relay FOR, conductor 68, alternate contact 69 of relay SL conductors 4:0 and 41 to ground at alternate contact 32 of relay AU and the answering supervisory lamp AS is lighted over this circuit. The replacing of the receiver at the called substation B opens the energizing circuit of the calling supervisory relay SR at the switchhoolr contacts and the closing of its normal contact 88 establishes a circuit for the calling supervisory lamp CS traced from battery through the lamp CS, normal contact 33 of relay RC, conductors 341 and 35 normal contact 36 of relay Ll), conductor 37, normal contact 38 of relay SR, conductors 39, 40 and 41 to ground at alternate contact 32 of relay AU, and the lamp CS is lighted over this circuit. The lighted answering and calling supervisory lamps AS and CS indicate to the operator of the cord C that the subscribers at the calling and called substations A and B have finished conversation and have replaced their receivers upon their respective switchhoolzs.

The relay SR upon deenergization closes an energizing circuit for the link disconnect relay LD traced from battery through the winding of relay LT), conductor 70,. alternate contact 71 of relay SL conductors 64 and 65, normal contact 61 of relay SR, conductor 66, normal contact 67 of relay FUR, conductor 68, alternate contact 69 of relay SL, conductors 40 and ll to ground at alternate contact 32 of AU. The relay LD energizes and opens its normal contact 8 interrupting the initial energizing circuit of the sleeve relay SL but the contact 8 of relay LD assuming its alternate position establishes a substitute energizcircuit for the relay SL independent of the cut oil relay CO traced from batter through winding 5 of relay SL its alt-ernat contact 9, conductor 7.. alternate contact 6, conductors 6d and 65, normal contact 61 of relay SR. conductor 66, normal contact 67 of relay FUR, conductor 68, its alternate contact 69, conductors l0 and 4:1 to ground at alternate contact 82 of relay AU. The relay SL remaining energized also maintains the relay LD energized over the circuit as previously described. The relay LT) energizes and opens its normal contact 86 which interrupts the initial circuit of the calling supervisory lamp CS but a substitute circuit is closed for the lamp CS traced from bat through the lamp CS. conductor T2, alte ve contact 36 of relay Ll), conductor 37', normal contact 360i relay SR, conductors 89, 40 and ll to ground at alternate contact 32 of relay AU.

The link disconnect rela If upon energizing opens its normal contacts 24 and 24 to disconnect the cord conductors from the call.- ing line, and as the cut oil relay CO is now at normal the calling subscriber may initiate a recall by removing his receiver which again brings about the energization of the line relay LE. to light the line signals S and the same operator who answered the original call may seize the recall or any one ot'a plurality of operators may seize it as is well understood from the previous description.

The operator noting-the two lighted signals AS and CS now removes the plugs AP and GP from the respective jacks J and J and the removal of the answerin plug AP from the jack J disconnects the answering end of the cord C from the calling line. The removal oi the calling plug GP irom jack J" opens the energizing circuit of the cut otl relay CO, and sleeve relays SL and SL The relay SL upon deenergizing opens its alternate contact 28 which allows the relay AU to restore and the opening of alternate contact 32 otrelay AU allows relays LD and to restore and also ellacesthe signals AS and CS. The apparatus used in establishing the connection above described is now at normal and available for establishing other connections.

l-laving described in detail the operation of 1 in which a calling l cal substation as r is connected to a called local substation B, 1 will now describe the operation of the circuit arrange cent illustratedin Fig. 1 in connection an h the circuitarrangement illustrated in Fig. 2. Fig. 2 when placed to he right of 1 illustrates a circuit connecion between the calling subscriber at the .nd a called subscriber at the substation D ermlnating at the distant exchange F.

aclt T5 terminating at her position and which leads to the distant exchange F and depresses one of the key plungers or the ringing key BK to impress ringing current over the trunk conductors 80 and 81 to actuate the drop signal DS at the distant exchange F. The insertion of the calling plug GP into the trunk jack TJ closes an enei Ling circuit for the sleeve relay SL' traced'froni ground through the resistance 82, sleeve contacts of the connected jack TJ and plug GP, through the winding of relay SL, conductorQT to battery through the windingot relay SL lne relay SL operates over this circuit but the relay SL does not due to the high resistance 82 in circuit with the relays SL and SL substation A terminating at the exchange E' AP of the cord circuit C in the incoming:

trunk jack TJ in response to the actuated drop signal DS at the dim-ant exchange as will now be describec. The operator of the cord C at the exchange E hav' g d r 'l a key plunger of the ringing l: y BK also closes the end spring 42 to energize the r ay RI over a circuit as previously described and the closing of alternate contact 59 of relay RI connects ringing current from the cons nected generator G over conductor alternate contact 50 of relay RL' tip contacts of the connected plug GP and trunk 'ack TJ conductor 80, windings a and c of the repeating coil RC, conductor 81, ring contacts of the connected jack TJ and plug GP to ground at alternate contact 53 of relay Ringing current is induced into the secondary windings and (Z of the repeating coil RC and through the Winding of the drop .nal DS whereby the signal DS operated. The operator at the distant exchange F in re sponse to the actuated drop signal IDS 1nserts the answering plug AP of the cord circuit G into the incoming trunk jack TJ and actuates her listening key LK to connect her operators set 0 to the cord conductors. The

insertion of the plug AP into the jack T5 closes the normally open auxiliary contact 83,

of the jack TJ which closes an energizing circuit for the calling supervisory relay SR, traced from battery through the lower Winding of relay SR, conductor 57, normal contact 53 of relay RI, ring contacts of the connected plug GP and trunk jack TJ, conductor 81, winding 0 of the repeating coil RC conductor 84, closed contact 83 of the jacl; TJ, conductor 85 winding a" of the repeat ing coil RC, conductor 80, tip contacts of the I connected jack TJ and plug OP. normal con tact of relay RI, conductor 58, alternate contact 59 of relay AU, conductor 60 to ground through the upper winding of relay SE. The relay SR upon energizing opens its normal contact 38 which opens the circuit of the supervisory signal CS which is now ct faced and notifies the operator of the cord C at the exchange E that the operator at the distant exchange F has answered the F now actuates her listening key LK to coin nect her operators set 0 and inquires the call. The operator of the cord 0 atthe exchangev scriberat the substation D that is wanted she inserts the'calling plug GP into the jack J of the called line and depresses the ringing key RK to impress ringing cii 'rent upon the called line from the connected generator G" and the subscriber at D response to his call signal removes his recei The subscriber at the substation A at the exchange Erand the subscriber at the substation D at the exchange F are now in conversational circuit which may be traced over the heavily marked conductors.

Upon the termination of conversation the subscribers replace their receivers upon their respective switchhooks and the replacing of the receiver at the called substation D at the distant exchange and the actuation of the hand generator thereat causes the current from the hand generator to actuate the clearring out signal COS of the cord circuit C at the exchange F. The operator noting the actuated clearing out signal removes the answering plug AP of the cord C from the jack TJ and the removal of the said plug again opens the contact 83 associated with the jack TJ. The opening of this contact 83 again opens the circuit of the calling supervisory relay SR and the relay SR upon deenergizing again closes its normal contact 38 to close a circuit for the calling supervisory signal CS. The signal CS is again lighted and gives the operator of the cord circuit C at the exchange E an indication that the subscriber at substation D at the distant exchange F has replaced his receiver and that the operator at the distant exchange has removed the plug AP from the jack TJ.

The replacing of the receiver at the calling substation A at the exchange E opens the energizing; circuit of the answering supervisory relay SR at the switchhook contacts and the closing of its normal contact 61 closes an energizing circuit for the flashing supervisory signal control relay FCR traced from battery through the upper winding 90 of relay FCR, conductor 91, normal contact 92 of the listening key LK, conductor 93, normal cone tact 71 oirelay SL conductors 64 and 65, normal contact 61 of relay SR, conductor 66, normal contact 67 of relay FUR, conductor 68, alternate contact 69 of relay SL, conductors 40 and 41 to ground at alternate contact 32 of relay AU. The relay F CR energizes over thiscircuit and the closure of its make before break contact 94 maintains the relay FUR energized the energizing, circuit being traced from ground at the make before break contact 94, conductor 66, normal contact 6i of relay SR, conductors and er, normal contact 71 of relay SL ,conductor 98,11ormal contact 92 of the key LK, conductor 91 to battery through the winding 90 of relay FCR. i The closing of alternate contact 95 of relay FOR also closes a circuit through its lower winding 96, traced from battery through the is seeking information. 1

of relay AU. The closing or" alternate contact 62 of rela F CR- closes a circuit throu h the lame Y 21 AS traced from battery through alternate contact 62, the lamp AS, conductors63, 6st nd 65, normal contact 61 of relay SR, conductor 66, to ground at the make'betore break contact 94 of relay F63. The relay energizes immediately upon the restoration'ot relay SR to normal and thus prevents the lamp AS from operating over a circuit through normal contact 62 or" relay FOR .as is the case in a connection between two local substations. The lamp AS is lighted over this circuit and the lighted na'l lamps AS and CS indicate to the o tor that conversation has terminateiil.

Assuming now that the calling subscriber wishes information relative to the trunk connection-as to the charges, wrong: 11Ul11l31"01 inquiry of a similar nature,t1e removal of the .recelver at the substation A again energizes the answering supervisory lamp n8. The relay SB energizes and opens its nor-- mal contact '61 thereby opening the circuit throughthe upper winding 90 of relay FOR. but the relay FCR remains energized over a circuit which extends through its lower winding 96 as before described. The closing of alternate contact 61 ct relayS'R now closes a circuit through the answering supervisory lamp AS traced from battery, through alternate contact 62 of relay FUR, through the lamp signal AS, conductors 63, ea and 65, alternate contact 61 ot'rela'ySlt, conductor alternate contact 100 of relay FER, to ground through the constantly rotating int rrupter I. The answering supervisory lain; AS is flashed due'to theli'nterrupter I and gives'the operator of the cord Cat the exchange E a distinctive indication that the subscriber I e operator 0 cord '0 now actuates her li... -iing keylait to connect her operators set I) 'to'the cordconductors over conductors 12,113 and 101, 102. alternatecontacts 103 and 16% oit'the listening key LK, conductors 105,106,1aormail contacts 30 andgl'ot relay SL and conductors 1.9 and 21 to'the respective tipnndring conductors oi the cord C. The opening-of normal contact 98 otthe listening key LK opens the circuit through the winding 96 of relay F61 and'the relay deenergizes to open its alternate contacts 62 and 100 which interrupts the hashing-circuit of the lamp signal .135. The operator may now converse with the calling subscriber at A andtake care othis wants.

From the previous descriptionor" a connection between two subscril ers located in the exchange E it will be remembered that when the calling subscriber recalled the recall'appeared before a plurality of operators.

When a calling subscriber at E is connected with a subscriber at the distant enchange F the relay SL of the cord C at the exchange E fails to energize, as before pointed out, and as this relay controls the operation of the link disconnect relayno energizing circuit is esta lished for the relay LD when the callsubscriber at E replaces his receiver so that when a calling subsc iber wishes to recall on a local to toll connection as just described, the recall will appear only beforethe operator who supervised the connection. The operator may supervise the connection at all times through the use of her listening key Ll; which connects her set 0 to the cord conductors duri g the settin upperiod or while conversation is going on as the relay SL remains deenergized as before described. The operators set 0 is connected to thecord conductors through normal contacts 30 and 81 of relay SL and in the event that'the calling subscriberat A wishes to recall the original operator who-received the recall may take care of the wants of the recalling subscriber and also properly'supervise a localto toll connection as just described. When the operator notes the two lighted supervisory signals AS and GS she removes the plugs AP and C from the respective jacks J and TJ. lhe removal otthe plug CPfirom the jack Til allows relay SL .tovrestore to open'the circuit of relayieill. The relavAU restoring opens the circuit of relay FOR and eii'aces the lamp signals AS and CS. The removal of theplug AP from the ack J'opens'the circuit for the relays Si and CO and the apparatus used in establishing the connection between the subscriber at 2 and the subscriber at .l) in the distantenchange F is now at normal and available for establishing other connections.

While I have described any invention in connection with a certain circuit arrangement, '1 do not wish to belimited to the same, as modifications and changes may suggest themselves to those skilled in the art. therefore I desire to cover all such changes and modifications come within the spirit and scope of the appended claims.

Having described my invention what I claim .is new and desire to secure by United States Letters Patent is:

1. A. telephone system comprising local calling lines and called local and tell lines. an operators link circuit having a pair of connection terminals for interconnecting said calling local and called local, or toll lines. means in said link circuitcontrolled by said calling local line on a local to local connection for operatively disassociating itselttrom a connection terminal of said link circuit, said means being rendered ineffective when said local line is connected to a toll line.

2. A telephone system comprising local calling lines and called local and tolllines. an operators link circuit having a pair of connection terminals for interconnecting said calling local and called local and toll lines,

means in said link circuit controlled by said calling local line on a local to local connection for operatively disassociating itself from said link circuit, a supervisory signal in said link circuit lighted upon the operation of said means, and means in said link for rendering ineffective the said first means when said local line is connected to a toll line.

3. A telephone system comprising local calling lines and called local and tell lines. an operators link circuit having a pair of connection terminals for interconnecting said calling local and called local or toll lines, means in said link circuit controlled by said calling local line on a local to local connection for operatively disassociating said calling line from the said link circuit, a supervisory signal in said link circuit lighted upon the operaton of said means, means in said link circuit for rendering ineffective the said first means on a local to tell connection and for closing another circuit for said supervisory signal to cause said signal to be intermittently operated. I

4. A telephone system comprising local calling lilies and called local and toll lines, an operators link circuit having a pair of connecting terminals for interconnecting said calling local and called local or toll lines, a relay in said link responsive to the connection of a connecting terminal of said link to a called local line, means in said link controlled by said calling line on a local to lecal con nection and said relay for disassociating said calling line from a connection terminal of said line, said relay being ineffective when a connecting terminal of said link is connected With a toll line to render inetlective the calling lines control of said means.

5. A telephone system comprising local calling lines and called local and tell lines.

an operators link circuit having a pair of connecting terminals for interconnecting calling local and said called local and tell lines, a supervisory signal, a relay in said link responsive to the connection of a connect ing terminal of said link to a called local line, means in said link controlled by said calling line on a local to local connection through contacts of said relay for disassociating said calling line from the connecting terminal of said line, and lighting said supervisory sig nal, said relay being inoperative when a connecting terminal of said link is connected With a toll line whereby the calling lines control of said means is rendered inetlectivc.

6. A telephone system comprising local calling and called local and toll lines, an operators link circuit having a pair of connecting terminals for interconnecting said calling local and said called local and toll lines, a supewisory signal, a relay in said link responsive to the connection of a connecting terminal of said link to a called local line, means in said link controlled by said calling line on a local to local connection through contacts of said relay for disassociating said calling line from the connecting terminal of said line and lighting said supervisory signal, said relay being inoperative When a connecting terminal of said link is connected With a toll line to render ineffective the calling lines control of said means and means operating through said relay on a local to tell connection to cause said supervisory signal to be intermittently operated.

7. A telephone system including a calling subscribers line, called lines of different character, a signal individual to said calling line, a link circuit for connecting said calling line to said called lines, a signal individual to said link circuit, and subscriber controlled means for operating said first signal it said link clreuit is used to connect said calling line to a called line of one character and for intermittently operating the second of said signals if said link circuit is connected to a called line of a difierent character.

8. A telephone system including a calling subscribers line, called lines of different character, a signal individual to said calling line, a link circuit for connecting said calling line to said called lines, a signal individual to said link circuit, and subscriber controlled means for operating said first signal it said link circuit is used to connect said calling line to a called line of one character and for operating the second of said signals if said link circuit is connected to a called line of a different character to denote a recall.

9. A telephone system including a calling subscribers line, called lines of different character, an operators link circuit having a pair of connecting terminals for interconnecting said calling and called lines, an operators telephone set, relay means in said link circuit for connecting said operators telephone set to said link circuit, other relay means for disconnecting said telephone set from said link circuit, an operators listening key for connecting said telephone set and said link cir cuit, relay means in said link circuit responsaid link circuit.

10. A telephone system comprising local calling lines and called local andtoll lines, an I operators link circuit having a pair of connecting terminals for interconnecting said calling and called lines, an operator-7s telephone set, relay means in said link circuit for automatically connecting said operators telephone set to said link circuit, said means responsive to the connection of a connecting terminal of said link circuit to said calling line, relay means in said link circuit responsive to set from said link circuit, means in said the connection oi a connecting terminal of said link circuit to a called line for automatically disassociating said operators telephone link circuit for connecting said operators telephone set to saidhnk circuit subsequently to the operation of said second relay means, said means being rendered 'ineliective when said connecting terminal .18 connected to a called local line.

11. A telephone system comprising local calling lines and called local and toll lines, an operators link circuit having a pair of connecting terminals for interconnecting said calling local andcalled local or toll lines, an operators telephone set, relay means in said link circuit for automatically connecting said operators telephone set to said link circuit, relay means in said link circuit torautoniatically disassociating said operators telephone set from said link circuit, an operators listening key for connecting said operators set and said link circuit subsequently to the operation of said second relay means, means in said link circuit responsive to theconnection of a connecting terminal'to a called local line whereby the said listening key is rendered ineiiective to connectsaid operators telephone set and said link circuit.

12. A telephone system comprising local calling lines and calledlocal and toll lines,an operators link circuit having a pair of connecting terminals for interconnecting said calling local and called'local or .toll lines, an operators telephone set,relay means in said link circuit for connecting said operators telephone setand said link circuit, other relay means for disconnecting said telephone set and said link circuit, an operators listening key for connecting'said-operators set to said link circuit when one ot 'saidconnecting terminals is connected to a called toll line, means i in said link circuit responsive to the connection of a connecting terminal to-a called local line for rendering ineffective said listening key.

Signed by me at Chicago, in the county of Cook and State of Illinois, this 18th day at December, 1926.

-BE-R'l A. WALLACE. 

